HI Experts,
As i Know ,ODS stores only current data like OLTP.Then y do we need to create ODS..We can access data directly from OLTP..right?
pls explain me in detail the differences bwetwen ODS and OLTP....

Previous definition is a bit too simplified in my opinion. ODS doesn't necessarily contain denormalized data and it can be a 1-on-1 copy of the OLTP system, periodically updated, just for reporting and analysis. In that case, the ODS contains just as much historical data as the OLTP does.

Reasons to use an ODS include: performance/capacity (reporting on an ODS doesn't interfere with the daily use of the OLTP), tuning on database level (if correctly tuned, OLTP is for fast retrieval and update of a relatively small number of records, by a lot of users, ODS is tuned for retrieval of loads of records by less users). Furthermore, you can add lookup tables, pre-computed aggregates, etc.

But bottom line is: if you can't think of a reason why you would need an ODS, then you don't need one!